The present invention relates to a head-mounted image display apparatus which is retained on the observer's head. More particularly, the present invention relates to a head-mounted image display apparatus which is capable of selectively displaying images of two different sizes, i.e., a normal size and a wide size.
One type of conventional head-mounted image display apparatus is capable of selectively displaying images of two different sizes, i.e., a normal size having an aspect ratio (i.e., the ratio of width to height of the image frame) of 4:3, and a wide size having an aspect ratio of 16:9, for example. As shown in FIG. 6(a), a conventional head-mounted image display apparatus employs a display device 21 having a display area of the normal size, i.e., the aspect ratio of 4:3. When an image of the wide size is to be displayed on the display device 21, the top and bottom 22 of the display surface of the display device 21 are cut so that the aspect ratio of 16:9 is attained. With this method, however, the pixel utilization efficiency is low, and the image frame is reduced in size.
One measure which has heretofore been taken to deal with the above-described problem is to use a circular display device 23, as shown in FIG. 6(b), so that even when the aspect ratio is changed from the normal size 24 to the wide size 25, the display image frame does not reduce in size (see Japanese Patent Application Laid-Open (KOKAI) No. 04-177986 (1992)).
According to another conventional measure, an image of the wide size is displayed in a compressed form on the display device 21 of the normal size, and the compressed image is enlarged to the wide size for observation by using an optical system including a concave cylindrical mirror 26 and a concave mirror 27, or a cylindrical Fresnel lens 28, as shown in FIGS. 6(c) and 6(d) (see Japanese Patent Application Laid-Open (KOKAI) No. 04-97671 (1992)).
However, when a circular display device is used as shown in FIG. 6(b), a part of the display surface is always left unused. Therefore, the pixel utilization efficiency is low. In the case of using an optical system that enlarges the image frame in one direction as shown in FIGS. 6(c) and 6(d), it is necessary to remove the optical system from the position in front of the display device when an image of the normal size is to be displayed. Thus, the conventional technique involves problems in terms of handling.